Mine is 1280 x 800. Although I also think it would help to have a bigger window displaying more info at the same time, I also like the idea of the window not being too big so I can open several recipes and compare them side by side.

Why not render the whole interface in SVG or some other vector scaling output so it draws to whatever screen size that the user has? That way it'll look great on every screen. You'll just have to avoid bitmaps.. and there are ways to use Adobe Illustrator to convert raster images to vector drawings, so if you need a few things converted - that is possible also (I could help here if necessary). If you had a general Vector display API, this would nail everything down from the start - then just vector scale it to fit any screen.